1. Field of the Invention
The present invention relates to strobe light circuits, and more particularly to D. C. powered circuits adapted for use with discharge tubes.
2. Description of the Prior Art
The use of strobe lights for various purposes has been known in the past. Quite often, in order to conserve the total power consumed, strobe lights are used as warning or safety markers, particularly around construction sites close to a highway. In these applications such warning lights are frequently left unattended over long periods of time and efficient consumption of stored energy is therefore of paramount importance. In the past various strobe light circuits adapted for this use have been developed where a discharge tube periodically dissipates the power charged up in a capacitor. To concurrently charge up the capacitor and trigger the tube an oscillator circuit was frequently used in such circuits.
Circuits of this kind have been also utilized in entertainment devices which in addition to power considerations also entail some control over strobe accuracy.
Generally a discharge tube requires a decreasing anode to cathode voltage as the trigger voltage increases. As the frequency of the trigger voltage increases, the required anode to cathode voltage also decreases. These phenomena have not been adequately utilized in the past with the result that all prior circuits have been of relatively high complexity.
SUMMARY OF THE INVENTION
Accordingly it is the general purpose and object of the present invention to utilize the reduction of trigger voltage with increasing anode to cathode voltage in a discharge tube to best advantage and thus implement a circuit requiring few parts.
Yet another object of the invention is to provide a D. C. powered strobe light circuit wherein the trigger elements are reduced to a single additional winding in a transformer-oscillator.
Yet further objects of the invention are to provide a strobe light circuit which is easy to produce, convenient to use and requires few parts.
Briefly these and other objects are accomplished within the present invention by utilizing a blocking oscillator having a oscillator transformer connected in a conventional circuit, with the primary thereof in the collector leg of the oscillator transistor and the second leg connected across the base-emitter circuit. This manner of connection provides the necessary positive feedback driving the transistor between its limits. In this conventional configuration, the base-emitter circuit branch is capacitively coupled and therefore when the transistor is off there is usually some reverse current. It is this reverse current that has been a source of energy loss. To conserve energy in this part of the circuit it is presently contemplated to include a forward biased diode connected across said capacitor. This implementation reduces the reverse current transient during the off time of the transistor, with a consequent power saving. The unstable oscillatory characteristics of the circuit, however, are still maintained in the positive current direction.
This circuit configuration is then further modified by providing a fourth winding in the transformer coupled to the collector winding. The upper end of this fourth winding is then directly applied to the trigger connection of the discharge tube. Concurrently the third winding of transformer is connected to charge across a diode, the main storage capacitor connected across the anode to cathode circuit. Thus, what has been heretofore performed by relatively complex circuitry is now achieved by the simple expedient of one additional winding.
By proper selection of the winding turns of the elements of this transformer it is furthermore possible to achieve any desired ratio between the anode to cathode voltage and the trigger voltage. The result is an increasing trigger voltage with an increase in the anode to cathode potential which produces a very consistent triggering frequency. Furthermore, should the trigger voltage vary from flash to flash the combined parameters compensate to produce reliable and consistent triggering.